A typical plastics tubular container for a paste material, such as toothpaste, is made by forming a flexible tube and cutting the tube to length, and then assembling the tube to an injection moulded shoulder piece with an outlet nozzle. The tube may be extruded or may be formed by shaping a flat plastics strip around a mandrel so that the longitudinal edges of the strip are brought together during the shaping process and are welded together as the strip is advanced. The tube formed in this manner is typically substantially round or oval in cross-section and one end of the tube has a shoulder piece with an outlet nozzle welded thereto and the other end of the tube will be closed, after filling of the tube, in a sealed `fish-tail` type end.
When the tubular body is formed from laminate strip, which is typically 300 microns (0.012") thick, the overlapping edges of the strip form irregularities in the thickness of the sidewall where they overlap, together with a step on both the internal and external surfaces of the tube. The known tube shoulder pieces are formed from a high density polyethylene material typically having a melt flow index in the range of 4-10, and the tube formed from the laminated strip typically comprises an aluminium foil barrier layer having an adhesive tie layer on each side thereof, with at least one layer of a polyethylene material over each adhesive layer. The tube is welded to the shoulder piece using high frequency welding techniques. In some cases the welds may be imperfect and this is in part due to the irregularities in the tube as previously described, which may cause problems in the welding of the moulded Shoulder to the tubular body. Defects frequently occur in the area where the overlapping edges are welded to the shoulder piece.
An increase in pressure applied during welding, or in the electrical power used in the welding process may improve the integrity of the welds produced and reduce the reject rate but unfortunately produce an assembly of inferior aesthetic appearance.